1. Field of the Invention
The present invention relates generally to methods of detecting colon cancer, and more particularly, to a method for detecting colon cancer using a marker, cathepsin E.
2. Related Art
The identification of molecular markers and proteomic patterns in the inception and progression of colon cancer is a major goal in the management of this disease. In the search for sensitive and accurate markers of colon cancer, APCMin/+ mice (heterozygous for a chain-termination mutation in the 15th exon of the APC gene) are regarded as reliable models of spontaneous tumorigenesis, developing multiple intestinal adenomas that clinically mimic those observed in patients with familial adenomatous polyposis [1,2]. Published microarray data has quantified the changes in gene expression accompanying transformation of APCMin/+ intestinal epithelium from normal morphology to adenomas and carcinomas [3].
Native catE is an intracellular, non-lysosomal, aspartic protease comprised of two disulfide-linked monomeric subunits of 42 kDa, although several mono- and dimeric proenzyme and glycosylated forms have been reported in expression systems and in vivo [4,5]. The monomeric form can be obtained under mild reducing conditions and is catalytically indistinguishable from the mature dimer [4]. The tissue distribution of the mammalian enzyme and its transcript are limited and most prevalent in the gastric epithelium [6], although relatively robust expression has also been noted in spleen, thymus, bladder, and erythrocyte membranes [7]. CatE is believed to function as a major component of the proteolytic processing machinery for antigen fragment presentation by then major histocompatibility complex, class II [8]. Pathophysiologically, increased catE levels in human gastric and pancreatic adenocarcinomas have been established [9-11]. However, a detectable increase in tissue or urine catE levels has not been established for the diagnosis or detection of colon cancer.
A non-invasive test, such as a urine test, has not yet been established for colon cancer. A need continues to exist in the medical arts for a reliable marker of colon cancer that may be used to detect and track the pathology of this disease.